PROJECT III - SUMMARY/ABSTRACT Orthotropic human liver transplantation is the primary therapy for end-stage liver disease and acute liver failure. However, ischemia and reperfusion injury (IRI), the inevitable consequence of the transplant process, is a key limitation. The cellular damage incurred by IRI occurs in about 20% of cases and can lead to primary non-function necessitating re-transplantation. Liver IRI also predisposes the recipient to both acute and chronic rejection and graft loss, as well as, decreasing the pool of transplantable organs. Seminal observations in murine models indicate that liver IRI is mediated by both the innate and adaptive immune systems. Little is known whether similar mechanisms are at play in human liver transplantation. Our central hypothesis is that identifying the continuum of innate and adaptive immune phenotypes during human liver transplant IRI will permit us to select, monitor and refine the practice of therapeutic interventions and hence improve liver transplant outcomes. Under Aim 1 we will determine the role of DAMP/Pattern Recognition Receptor (PRR) signaling in the activation of innate and adaptive immune responses in human OLT IRI. We hypothesize that IRI-stressed hepatocytes release the endogenous DAMPs that trigger TLR and other PRR signaling on innate myeloid cells, which then induce adaptive immunity via T cell activation. We will investigate whether effluents from IRI+ allografts trigger innate myeloid cell activation through TLR/PRR signaling. Furthermore, we will define the role of DAMPs within the IRI effluent in triggering myeloid cell activation and see if DAMPs alter T cell activation and polarization. Under Aim 2 we will delineate the pathological signature of human liver transplant IRI. We hypothesize that IRI leads to activation of hepatocytes and resident Kupffer cells and LSECs, and recruitment/activation of myeloid cells and circulating T cells in human liver allografts, and this pathological cascade will perpetuate damage to the graft. To prove this concept, we will establish a ?transcriptome? profile for IRI biopsies to better understand mechanisms of injury and characterize the acute and long-term pro-inflammatory profile of IRI and elucidate interactions between innate and adaptive immune cells in situ. Under Aim 3 we will determine the crosstalk between alloimmunity and IRI. We postulate memory T cells enhance inflammation and tissue injury in human liver transplant through antigen-dependent and antigen-independent mechanisms. We will therefore determine if allospecific T memory cells augment human liver IRI and also determine if IRI potentiates alloreactivity. Detailed insights into the interactions of the innate and adaptive immune system in human liver transplantation IRI will generate novel concepts to better understand the mechanistic underpinnings and to develop novel therapeutics to treat this major clinical problem.